I have to agree that Benjamina, the weeping fig, is the most finicky of all the ficus I have ever dealt with. They do not like to be moved much, unless you move them constantly believe it or not. Being inside will dehydrate them severly as Rockm mentioned. Also your air conditioner in 100 degree weather is probably pumping 35 degree air out to keep your home around 70 degrees, chilling your plant in the process and they do not like the cold. They (benjamina) have a lot of negative qualities for a Bonsai, they tend to grow really large leaves, even when outdoors or after being defoliated which either situation on any other Ficus will result in smaller leaf growth. They are also very prone to get weak with changes in water, I noticed this as I travel and take my plants with me. if it were mine I would defoliate it now so it spends energy shooting new growth instead of trying to repair damaged foliage, after defoliating it set it outside in the shade and do not water it for a few days until you notice it needs water, they can stand a drought better than being water logged, another trait of the Benjamina not shared by most other ficus. When it needs water soak it and wait until it needs it again, when it starts to swell new buds move it where it gets half day sun for a week or so and then when it looks good again get it in full sunlight.
I would bet that more than too much or too little water what is hurting that plant, judging by the look of the leaves, the plant has either been exposed to air freshener spray or cooking fumes this tends to poison or clog the foliage of Ficus easily. Those automatic oil spray air fresheners like Airwick and Glade sell tend to coat the foliage which prevents the foliage from "breathing" or allowing them to transpire through the leaves, cooking oils do the same thing too, the things like Pam or any of the non stick sprays as they float through the air landing on your plant.
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